Interplay between interferon regulatory factor 1 and BRD4 in the regulation of PD-L1 in pancreatic stellate cells

Kazumi Ebine,Thao N Pham,Sam Grimaldo,Meng Shang,Paul J Grippo,Katharine A Collier,David J Bentrem,Krishan Kumar,Mario A Shields,Rosa F Hwang,Brian T Decant,Daniel R Principe,Raul Urrutia,Hidayatullah G Munshi

doi:10.1038/s41598-018-31658-1

Abstract

The fibrotic reaction is a characteristic feature of human pancreatic ductal adenocarcinoma (PDAC) tumors. It is associated with activation and proliferation of pancreatic stellate cells (PSCs), which are key regulators of fibrosis in vivo. While there is increasing interest in the regulation of PD-L1 expression in cancer and immune cells, the expression and regulation of PD-L1 in other stromal cells, such as PSCs, has not been fully evaluated. Here we show that PSCs in vitro express higher PD-L1 mRNA and protein levels compared to the levels present in PDAC cells. We show that inhibitors targeting bromodomain and extra-terminal (BET) proteins and BRD4 knockdown decrease interferon-γ (IFN-γ)-induced PD-L1 expression in PSCs. We also show that c-MYC, one of the well-established targets of BET inhibitors, does not mediate IFN-γ-regulated PD-L1 expression in PSCs. Instead we show that interferon regulatory factor 1 (IRF1) mediates IFN-γ-induced PD-L1 expression in PSCs. Finally, while we show that BET inhibitors do not regulate IFN-γ-induced IRF1 expression in PSCs, BET inhibitors decrease binding of IRF1 and BRD4 to the PD-L1 promoter. Together, these results demonstrate the interplay between IRF1 and BRD4 in the regulation of PD-L1 in PSCs.

Highlights

PD-L1 expression is seen in a number of human cancers, with increased expression of PD-L1 by cancer cells in some tumor types can be associated with responses to antibodies targeting PD-1/PD-L11
We show that pancreatic stellate cells (PSCs) express higher PD-L1 mRNA and protein levels compared to the levels present in pancreatic ductal adenocarcinoma (PDAC) cells
Since activated PSCs are the predominant fibroblasts present in the pancreatic stromal reaction[5], and the immune cells are very likely to encounter these cells in vivo, we evaluated expression of PD-L1 in an immortalized PSC cell line and in primary PSCs isolated from human PDAC tumors using the outgrowth assay[19]

Summary

Introduction

PD-L1 expression is seen in a number of human cancers, with increased expression of PD-L1 by cancer cells in some tumor types can be associated with responses to antibodies targeting PD-1/PD-L11. The BET proteins, which include BRD2, BRD3, BRD4, and the testis-specific BRDT, regulate transcription of genes involved in several human diseases[8,9]. These proteins bind to acetylation motifs present in histones and enable recruitment of transcription factors www.nature.com/scientificreports/. While BET inhibitors were recently shown to repress PD-L1 expression in lymphoma and ovarian cancer cells[14,15], the contribution of BET proteins to the regulation of PD-L1 expression in PSCs has yet to be evaluated. These results demonstrate the interplay between IRF1 and BRD4 in the regulation of PD-L1 in PSCs

Methods

Results

Conclusion